Can light drive a chemical process that is energetically uphill? A 2026 Nature Chemistry study provides a useful real-world example. Researchers reported artificial photosynthetic reduction of dinitrogen to ammonia using water as the terminal electron donor, iron(II) salts, a molybdenum catalyst and ultraviolet light. The overall process was calculated to be endoergonic by 329.2 kJ mol−1, while the system converted part of the absorbed light energy into chemical energy.
For Class 11 students, this is an excellent bridge between textbook thermodynamics and modern chemistry: an energetically demanding reaction can proceed when energy is supplied from outside—in this case, by light.
What did the researchers actually report?
The study describes a light-driven system in which inexpensive iron(II) salts absorb ultraviolet C light and generate solvated electrons. These electrons help reduce a molybdenum catalyst, which then participates in nitrogen reduction. The iron(III) ions formed in the process also absorb ultraviolet light and can be reduced back to iron(II) while water is oxidized.
The authors reported ammonia formation from dinitrogen in water at normal temperature and pressure with a photochemical quantum yield of about 5.0%. At elevated dinitrogen pressure, the reported quantum yield increased to 10.8%. They also calculated a 7.6% light-to-chemical energy conversion efficiency.
Source: D. Zidouhia, T. Tassaing, N. Penin, E. Grau and D. M. Bassani, “Artificial photosynthetic reduction of nitrogen to ammonia at room temperature using natural seawater,” Nature Chemistry (2026). Read the paper.
What does “endoergonic” mean?
An endoergonic process requires a net input of free energy. In simple terms, the products are not reached spontaneously from the reactants under the stated conditions unless energy is supplied from outside the reacting system.
This is different from saying that a reaction is “impossible.” Thermodynamics tells us whether a process is energetically favourable under specified conditions; it does not say that an unfavourable process can never occur. If an external energy source is coupled to the process, the chemistry can be driven forward.
In this research, light is the external energy source. The experiment therefore becomes a modern illustration of a principle students encounter in thermodynamics: an energetically uphill transformation can be achieved when it is coupled to a suitable energy input.
Why is light especially useful in this type of chemistry?
Light can promote electrons into higher-energy states and initiate photochemical electron-transfer events. In the reported system, ultraviolet irradiation of iron(II) salts generates solvated electrons. Those electrons are then used in the catalytic chemistry associated with nitrogen reduction.
This makes the process more than a simple “heat the reaction” example. It shows that energy can enter a chemical system in different forms. Thermal energy, electrical energy and radiant energy can all be relevant in different chemical technologies.
Thermodynamics versus kinetics: do not confuse them
This research is also useful because it reinforces a distinction that causes frequent mistakes in Class 11 and JEE preparation.
Thermodynamics asks: Is the process energetically favourable under the stated conditions?
Kinetics asks: How fast can the process occur, and through what pathway?
A reaction can be thermodynamically favourable but very slow. A reaction can also be thermodynamically unfavourable but still be driven when energy is supplied. Catalysts can change the pathway and rate, but they do not by themselves make an energetically uphill overall process thermodynamically downhill.
In the reported nitrogen-fixation system, the catalyst and iron redox chemistry help create a workable reaction pathway, while light supplies the energy needed to sustain the overall photosynthetic process.
How does this connect to Gibbs energy in Class 11?
In school thermodynamics, the Gibbs energy criterion is commonly used to discuss spontaneity at constant temperature and pressure. A process with a positive Gibbs energy change requires coupling or external energy input to proceed in the desired direction.
The paper describes the overall ammonia-forming process as endoergonic by 329.2 kJ mol−1. For classroom purposes, the important idea is not to treat that number as an isolated fact to memorize. The useful question is: Where does the required energy come from?
Here, the answer is light.
That is exactly the kind of reasoning students should develop: whenever a process is energetically uphill, identify the external energy source or coupled process that makes it possible.
Why this matters beyond one research paper
Artificial photosynthesis tries to use light to make energy-rich chemicals from abundant raw materials. Natural photosynthesis uses sunlight to drive chemical transformations that would not simply occur on their own at useful rates and extents. Artificial systems attempt to reproduce parts of that logic using designed catalysts and photochemical cycles.
The present research is interesting because it combines:
- light absorption,
- electron transfer,
- Fe(II)/Fe(III) redox cycling,
- transition-metal catalysis,
- water oxidation, and
- nitrogen reduction.
For students, that means one modern experiment connects several chapters that are often studied separately.
Class 11 and JEE concept checks
- If a process is endoergonic, is it impossible?
No. It requires a net energy input or coupling to another process. - Does a catalyst change the thermodynamic energy requirement of the overall process?
No. A catalyst mainly changes the reaction pathway and activation barrier; it does not change the initial and final thermodynamic states. - What is the external energy source in this artificial photosynthetic system?
Ultraviolet light. - Why is the reported light-to-chemical conversion efficiency important?
It indicates how much of the incident light energy is stored as chemical energy in the products/process. - Which redox pair appears in the reported photochemical cycle?
Fe(II)/Fe(III).
A useful exam-style reasoning question
Question: A chemical transformation is thermodynamically uphill under the reaction conditions, but researchers are able to carry it out using a photocatalytic system. Does this violate the laws of thermodynamics?
Answer: No. The reaction system receives energy from light. Thermodynamics is not violated because the external energy input is part of the complete energy balance.
What students should remember
The main lesson is simple: thermodynamically unfavourable does not mean chemically impossible. It means the desired transformation needs an appropriate energy source or coupling strategy. Modern photochemistry provides many examples in which light supplies the energy required to create useful chemical products.
This is one reason I encourage students to connect textbook thermodynamics with real research. The equations become much easier to understand when we see what chemists are actually trying to accomplish.
Frequently Asked Questions
Is an endoergonic reaction the same as an endothermic reaction?
No. Endoergonic refers to free-energy change, whereas endothermic refers to enthalpy change. A process can involve different signs of enthalpy and entropy, so the two terms should not be used interchangeably.
Can light make a non-spontaneous reaction occur?
Light can supply energy and create excited states or energetic electrons that allow an otherwise unfavourable transformation to proceed through a photochemical pathway.
Does the molybdenum catalyst supply the energy?
No. The catalyst helps provide a reaction pathway. The energy input in the reported system comes from light.
Is this already an industrial replacement for conventional ammonia production?
The paper reports a research-stage photochemical system. The source material does not establish industrial readiness, so it should be treated as a proof-of-concept research development rather than a commercial replacement.
About the author: Lalit Kumar Mishra is a Chemistry Educator, Student Success Mentor and Author, Founder of Topper Formula and Creator of The Clarity Blueprint Method™. He writes Science books for Classes 6–10 covering Physics, Chemistry and Biology, and Chemistry books for Classes 11–12 and JEE/NEET covering Physical, Inorganic and Organic Chemistry.